Halide perovskites have rapidly become a front runner in the area of cost-effective semiconducting materials for thin film photovoltaics, attaining certified 20.1% efficiency for single junction devices. These halide perovskites typically have a general chemical formula of AMX3, where A represents a cation, M a metal ion and X either a single halide or a mixture of halides. For photovoltaic applications, the cation is typically an organic cation but may in some cases also be an inorganic cation. Examples include the single halide methylammonium lead triiodide (CH3NH3PbI3) and its mixed halide variant CH3NH3PbI3-xClx, as well as the all inorganic CsSnI3. These semiconductors display many interesting characteristics, such as being solution-processable, having a controllable and direct band gap, and being relatively tolerant to defects. Solution deposition in either one or two steps has led to devices showing high performance and presents a viable option for large scale manufacturing in the commercial market. Beyond photovoltaics applications, many other uses employing a variety of perovskite materials are known; examples include spintronic applications, light emitting diodes and lasers.
Single-step deposition of perovskite is the most promising cost-effective process available. The process however hinges on several aspects such as suspending the precursors in a solvent, coating the substrate quickly and uniformly, drying into a morphologically optimal film, and supporting perovskite formation. Control of fabrication processes and parameters remain therefore a challenge in the formation of the crystalline structure of a characteristic perovskite.
The majority of common solvents implemented in the art for deposition of perovskites are hazardous to handle, using toxic N,N-dimethylformamide (DMF) and dimethylacetamide (DMA), skin penetrating dimethyl sulfoxide (DMSO), or carcinogenic N-methyl-2-pyrrolidone (NMP). It is however important to account for occupational safety for operators in manufacturing and scientists in the lab, who may come into direct contact with or inhale the fumes of the solvents.
There is thus still a need within the art for good compositions for the fabrication of perovskites, which have low toxicity while retaining a high performance of the resulting devices.